370 BULLETIN 100, UNITED STATES NATIONAL MUSEUM. 



thought it well to include here some photographs of S. sterea and of 



5. sladeni, not only to facilitate comparison between the two species 

 but also to permit of distinguishing both of them from a new species 

 which I am describing below under the name of S. sterilis. 



The arm spines are all very distinct in S. sterea, while in S. sladeni 

 the secondary spines are united into a sort of fringe (pi. 83, figs. 3, 



6, 7; see also Matsumoto '17, figs. 71, 72). The very marked median 

 prominence which the first under arm plates show in S. sladeni is 

 also very characteristic of this species. In the specimen of S. sterea 

 which I have at hand the two first under arm plates have the 

 median region very swollen, thus giving a first indication of that 

 keel which becomes so developed in S. sladeni. 



In both species the radial shields have the same shape, and the two 

 shields of each pair are very strongly divergent and very broadly 

 separated inwardly, and their respective median lines form with each 

 other a very obtuse angle. 



STEGOPHIURA STERILIS, new species. 



Plate 83, figs. 8-11. 



Locality. Albatross station 5301; China Sea, in the vicinity of 

 Hongkong (lat. 20 37' 00" N., long. 115 43' 00" E.) ; 380 meters 

 (208 fathomsi) ; August 8, 1908 ; gy. M., S. 



Thirty-two specimens (Cat. Nos. 41379, U.S.N.M.). 



Description. The diameter of the disk varies between 12 mm, 

 and 15 mm. In the specimen of which I give photographs (pi. 

 83, figs. 8-11) the diameter of the disk is 15 mm., and the arms are 

 from 45 mm. to 50 mm. in length. The two surfaces of the disk 

 are flattened, and they are united by rounded borders; the height 

 is 4 mm. The arms are almost as high as broad, and their section 

 is a triangle with a rounded apex ; their width at the base is 4 mm.,, 

 and this width diminishes rather slowly to the tip. 



The dorsal surface of the disk is covered with rather numerous, 

 unequal, irregular, polygonal or rounded plates, among which can 

 be distinguished a large pentagonal dorso-central with the angles 

 and the sides rounded and five primary radials each separated from 

 it by a small plate. These primary radials stand out less by their 

 size, which is not greater than that of the other plates of the disk, 

 than by their slightly darker coloration and rather peculiar form; 

 they are pentagonal, narrow, and almost three times as long as 

 broad, with an obtuse proximal angle and a straight distal border. 

 The other plates are irregularly arranged. In the median radial 

 line there is a rather large triangular plate separating the proximal 

 extremities of the two radial shields of each pair. In the iiiterradii 

 there are usually four rows of plates between the radial shields, and 



